1. Field of the Invention
The present invention relates to a pressure sensor utilizing the magnetostriction effect of an amorphous magnetic alloy.
2. Description of the Related Art
A pressure sensor utilizing the magnetostriction effect of an amorphous magnetic alloy (which was invented by a group including one of the inventors of he present invention) is disclosed in the U.S. Pat. No. 4,938,069.
Referring to FIG. 8, such a conventional pressure sensor will be described. FIG. 8 is a cross sectional view of a pressure sensor 55.
The pressure sensor 55 includes a cylindrical main body 41. The main body 41 includes a pressure chamber 43 for conveying a pressure and a hollow section 46. The pressure chamber 43 and the hollow section 46 have an identical diameter with each other. A part of the main body 41 enclosing the pressure chamber 43 is a deformable section 44 which is deformable when being supplied with a pressure. A part of the main body 41 enclosing the hollow section 46 is a non-deformable section 45 which is not deformable when being supplied with a pressure. The main body 41 has a pressure inlet 42 an at end thereof, and an outer peripheral surface of the pressure inlet 42 is provided with a screw thread 52 for securing the main body 41 to, for example, a container (not shown), the inner pressure of which is to be detected. The pressure chamber 43 is in fluid communication with the inside of the container.
An amorphous magnetic alloy member 47 is adhered on a part of the outer peripheral surface of the main body 41 to cover both of the deformable section 44 and the non-deformable section 45. The amorphous magnetic alloy member 47 is adhered by an adhesive agent including an imide material. When the volume of the deformable section 44 changes in accordance with a change in the inner pressure of the pressure chamber 43, the permeability of the amorphous magnetic alloy member 47 also changes.
The main body 41 provided with the amorphous magnetic alloy member 47 is enclosed by a bobbin 50. A pressure detection coal 48 formed of a wire winding and a dummy coil 49 are provided at the outer peripheral surface of the bobbin 50. The pressure detection coil 48 is located at a position corresponding to the deformable section 44, and the dummy coil 49 is located at a position corresponding to the non-deformable section 45. The pressure detection coil 48 and the dummy coil 49 are both connected to a detection unit 53. The detection unit 53 detects a change in the inductance of the detection coil 48 using the inductance of the dummy coil 49 as a reference value, thus to detect an inner pressure of the pressure chamber 43 based on the above-mentioned change. The change in the inductance of the pressure detection coil 48 corresponds to a change in the permeability of the amorphous magnetic alloy member 47. A yoke 51 is attached to the main body 41 by a screw (not shown) to cover the pressure detection coil 48 and the dummy coil 49.
A pressure sensor 55 having the above-described structure operates in the following manner.
The inner pressure of the container to which the pressure sensor 55 is secured is introduced to the pressure chamber 43 through the pressure inlet 42 to apply a stress to expand the pressure chamber 43. As a result, the deformable section 44 is deformed, and thus a part of the amorphous magnetic alloy member 47 covering the deformable section 44 is also deformed. By such deformation, the permeability of the above-mentioned part of the amorphous magnetic alloy member 47 changes due to a reverse magnetostriction effect in the amorphous magnetic alloy. Such a change in the permeability is detected by the detection unit 53 as a change in the inductance of the pressure detection coil 48. By contrast, the inductance of the dummy coil 49, which is located around the non-deformable section 45, does not change. The detection unit 53 obtains the difference between the inductances of the pressure detection coil 48 and the dummy coil 49, thereby detecting the pressure.
In such a conventional pressure sensor 55, the adhesive agent including an imide material is deteriorated by thermal shock and humidity, and thus the amorphous magnetic alloy member 47 peels off.
Further, when a plurality of pressure sensors 55 were produced and evaluated, there was non-uniformity in both of the outputs from the pressure detection coil 48 and the outputs from the dummy coil 49. Accordingly, the output characteristics of each of the pressure sensors are required to be corrected by the detection unit 53.
Still further, since provision of the bobbin 50 and the yoke 51 increases the diameter of the entire pressure sensor 55, reduction in the size is limited.